Skip to content

T1205 Traffic Signaling

Adversaries may use traffic signaling to hide open ports or other malicious functionality used for persistence or command and control. Traffic signaling involves the use of a magic value or sequence that must be sent to a system to trigger a special response, such as opening a closed port or executing a malicious task. This may take the form of sending a series of packets with certain characteristics before a port will be opened that the adversary can use for command and control. Usually this series of packets consists of attempted connections to a predefined sequence of closed ports (i.e. Port Knocking), but can involve unusual flags, specific strings, or other unique characteristics. After the sequence is completed, opening a port may be accomplished by the host-based firewall, but could also be implemented by custom software.

Adversaries may also communicate with an already open port, but the service listening on that port will only respond to commands or trigger other malicious functionality if passed the appropriate magic value(s).

The observation of the signal packets to trigger the communication can be conducted through different methods. One means, originally implemented by Cd00r 5, is to use the libpcap libraries to sniff for the packets in question. Another method leverages raw sockets, which enables the malware to use ports that are already open for use by other programs.

On network devices, adversaries may use crafted packets to enable Network Device Authentication for standard services offered by the device such as telnet. Such signaling may also be used to open a closed service port such as telnet, or to trigger module modification of malware implants on the device, adding, removing, or changing malicious capabilities. Adversaries may use crafted packets to attempt to connect to one or more (open or closed) ports, but may also attempt to connect to a router interface, broadcast, and network address IP on the same port in order to achieve their goals and objectives.436 To enable this traffic signaling on embedded devices, adversaries must first achieve and leverage Patch System Image due to the monolithic nature of the architecture.

Adversaries may also use the Wake-on-LAN feature to turn on powered off systems. Wake-on-LAN is a hardware feature that allows a powered down system to be powered on, or woken up, by sending a magic packet to it. Once the system is powered on, it may become a target for lateral movement.12

Item Value
ID T1205
Sub-techniques T1205.001, T1205.002
Tactics TA0005, TA0003, TA0011
Platforms Linux, Network, Windows, macOS
Version 2.4
Created 18 April 2018
Last Modified 19 October 2022

Procedure Examples

ID Name Description
S0220 Chaos Chaos provides a reverse shell is triggered upon receipt of a packet with a special string, sent to any port.11
S0641 Kobalos Kobalos is triggered by an incoming TCP connection to a legitimate service from a specific source port.1314
S0664 Pandora Pandora can identify if incoming HTTP traffic contains a token and if so it will intercept the traffic and process the received command.8
S0587 Penquin Penquin will connect to C2 only after sniffing a “magic packet” value in TCP or UDP packets matching specific conditions.109
S0446 Ryuk Ryuk has used Wake-on-Lan to power on turned off systems for lateral movement.1
S0519 SYNful Knock SYNful Knock can be sent instructions via special packets to change its functionality. Code for new functionality can be included in these messages.3
S0221 Umbreon Umbreon provides additional access using its backdoor Espeon, providing a reverse shell upon receipt of a special packet.12
S0430 Winnti for Linux Winnti for Linux has used a passive listener, capable of identifying a specific magic value before executing tasking, as a secondary command and control (C2) mechanism.15


ID Mitigation Description
M1042 Disable or Remove Feature or Program Disable Wake-on-LAN if it is not needed within an environment.
M1037 Filter Network Traffic Mitigation of some variants of this technique could be achieved through the use of stateful firewalls, depending upon how it is implemented.


ID Data Source Data Component
DS0029 Network Traffic Network Connection Creation
DS0009 Process Process Creation


  1. Abrams, L. (2021, January 14). Ryuk Ransomware Uses Wake-on-Lan To Encrypt Offline Devices. Retrieved February 11, 2021. 

  2. AMD. (1995, November 1). Magic Packet Technical White Paper. Retrieved February 17, 2021. 

  3. Bill Hau, Tony Lee, Josh Homan. (2015, September 15). SYNful Knock - A Cisco router implant - Part I. Retrieved October 19, 2020. 

  4. Graham Holmes. (2015, October 8). Evolution of attacks on Cisco IOS devices. Retrieved October 19, 2020. 

  5. Hartrell, Greg. (2002, August). Get a handle on cd00r: The invisible backdoor. Retrieved October 13, 2018. 

  6. Omar Santos. (2020, October 19). Attackers Continue to Target Legacy Devices. Retrieved October 20, 2020. 

  7. Perry, David. (2020, August 11). WakeOnLAN (WOL). Retrieved February 17, 2021. 

  8. Lunghi, D. and Lu, K. (2021, April 9). Iron Tiger APT Updates Toolkit With Evolved SysUpdate Malware. Retrieved November 12, 2021. 

  9. Baumgartner, K. and Raiu, C. (2014, December 8). The ‘Penquin’ Turla. Retrieved March 11, 2021. 

  10. Leonardo. (2020, May 29). MALWARE TECHNICAL INSIGHT TURLA “Penquin_x64”. Retrieved March 11, 2021. 

  11. Sebastian Feldmann. (2018, February 14). Chaos: a Stolen Backdoor Rising Again. Retrieved March 5, 2018. 

  12. Fernando Mercês. (2016, September 5). Pokémon-themed Umbreon Linux Rootkit Hits x86, ARM Systems. Retrieved March 5, 2018. 

  13. M.Leveille, M., Sanmillan, I. (2021, February 2). Kobalos – A complex Linux threat to high performance computing infrastructure. Retrieved August 24, 2021. 

  14. M.Leveille, M., Sanmillan, I. (2021, January). A WILD KOBALOS APPEARS Tricksy Linux malware goes after HPCs. Retrieved August 24, 2021. 

  15. Chronicle Blog. (2019, May 15). Winnti: More than just Windows and Gates. Retrieved April 29, 2020. 

  16. Jamie Harries. (2022, May 25). Hunting a Global Telecommunications Threat: DecisiveArchitect and Its Custom Implant JustForFun. Retrieved October 18, 2022.